1 MAF sensor
2 Mark showing installation direction
Depending on the version, two different MAF sensors are used:
โข analog MAF sensor โ transmits an analog voltage signal to the PCM, where an analog/digital converter converts the signal for further processing.
โข digital MAF sensor โ an integrated circuit in the MAF sensor converts the measured signal directly into a digital signal.
Note: in Emission Standard IV vehicles, a digital MAF sensor is usually installed.
Location: in the intake manifold, directly behind the air cleaner.
The MAF sensor measures the air mass drawn into the engine. The MAF signal is used:
โข as a parameter for calculating the quantity to be injected and the time of injection,
โข for controlling the EGR quantity (closed control loop with EGR valve).
There is a MAF sensor integrated into the IAT sensor (forms an NTC).
The IAT sensor corrects the MAF signal so that a more accurate measurement of the air mass can be achieved. If no separate IAT sensor is installed in the intake system downstream of the turbocharger, the IAT signal is used for calculating the turbocharger outlet temperature. In this version, the calculated value serves as a correction factor for calculating the air density downstream of the turbocharger.
Possible consequences of faults (MAF sensor)
If the signal fails, the PCM employs a substitute value, which is calculated from the engine speed and other values.
Possible consequences of faults (integrated IAT sensor)
In the event of a fault, the PCM performs the calculations using a substitute value. Furthermore, if installed, the thermo management system is controlled via a limited-operation map. If installed, the electric PTC booster heater is switched off.
Diagnosis (MAF sensor)
The monitoring system checks:
โข the sensor for short to ground/battery (by means of a limit range check) and open control loop.
โข the logical rise/fall rate of the signal, whereby intermittent faults are detected (e.g. loose connector contacts).
โข for plausibility of the signal (only 1.4L Duratorq-TDCi (DV) diesel engine, Emission Standard IV).
During a test cycle, the current maximum and minimum values are compared over a specified period for the limit range check.
If a value exceeds/falls below the calibrated range during this test cycle, the test cycle is deemed to be faulty and a test cycle counter is activated.
For a certain number of test cycles, the “sound” and “faulty” test cycles are recorded, evaluated and compared with one another.
The ratio of faulty test cycles to the total number of test cycles is calculated and compared. If the result exceeds a calibrated limit, a DTC is immediately stored. The increase check (for intermittent faults) works in a similar manner.
Malfunctions of the MAF sensor have a significant influence on exhaust gas emissions if the recirculated exhaust gas quantity cannot be controlled precisely. An excessively low EGR quantity causes a dramatic increase in the NOX emissions, on the other hand an excessively high EGR quantity causes an increase in diesel particulate emissions.
Therefore this is a MIL active component.
Possible diagnostic trouble codes:
โข MAF sensor: P0100, P0101, P0102, P0103, P0104.
Diagnosis (integrated IAT sensor)
The monitoring system checks the integrated IAT sensor:
โข for short circuit and open control loop (via the limit range check),
โข the logical rise/fall rate of the signal, whereby intermittent faults are detected (e.g. loose connector contacts).
In contrast, the integrated IAT sensor has only a slight influence on exhaust gas emissions and is therefore non MIL active.
Possible diagnostic trouble codes: P0110, P0112, P0113, P0114.